Filterability of sickle cells as a function of pO2: role of physico-chemical factors.

A rigidity index (RI) related to red blood cell deformability was measured by using the hemorheometre. The RI for 13 patients homozygous for sickle cell disease was 109 +/- 44 at 37 degrees C and at atmospheric pO2. The filtration time curve as a function of pO2 is biphasic for sickle cell suspensions. The pO2 at which filtration time is maximum, pO2max., correlated with the rigidity index measured at atmospheric pO2. This pO2max. value was very sensitive to small changes in physico-chemical parameters such as osmolality, pH, temperature, hematocrit, and cell density. Conditions which reduced the Hb S polymerization induced a leftward shift of pO2max.. The experimental curves are in agreement with theoretical models based on the presence of two abnormal cell types: filtrable "slow cells" and infiltrable "sickled cells".